1. Field of the Invention
This invention relates to communications techniques over a data network. More particularly, this invention relates to telephonic communication in which information is transmitted by synchronization of voice and data streams.
2. Description of the Related Art
TABLE 1Acronyms and AbbreviationsIETFInternet Engineering Task ForceIPInternet ProtocolITUInternational Telecommunication UnionITU-TITU Telecommunication Standardization SectorPDDPost-Dial DelayPSTNPublic Switched Telephone NetworkQoSQuality of ServiceRTSPReal Time Streaming ProtocolSIPSession Initiation ProtocolSS7Signaling System 7VoIPVoice over Internet Protocol
Voice over Internet Protocol (VoIP), also known as IP telephony, has become a preferred technique for routing of voice communications over the Internet and other data networks. Essentially, audio information flows primarily through a packet-switched data network, instead of traditional dedicated, circuit switched voice transmission lines. So long as the information remains in the data network, there is little marginal cost involved in processing the call. However, many such communications terminate in the public switched telephone network (PSTN), at which point charges may be incurred.
The popularity of VoIP has resulted in the development of many protocols dealing with various aspects of data formatting and communications, including call models and controls. Examples include ITU-T H.323, and ITU-T H.225. During the last decade, the IETF Session Initiation Protocol (SIP) has become an increasingly important signaling protocol for VoIP communications. SIP is formally defined in RFC 3261, available at the URL “http://www.ietf.org/rfc/rfc3261.txt”.